Device for electrically-recording telephonic sounds and conversations and system therefor



Nov. 25, 1930. M. J. JOHNSON 1,782,619

DEVICE FOR ELECTRICALLY RECORDING TELEPHONIC SOUNDS AND CONVERSATIONS AND SYSTEM THEREFOH Filed May 25. 1927 2 Shoots-Shoot 1 INVENTOR. Mmgfre JJobman,

Nov. 25, 1930. M. J. JOHNSON 1,782,519 DEVICE FOR ELHGTRICALLY RECORDING TELEPHONIC SOUNDS AND CONVERSATIONS AND SYSTEI THEREFOR Filed llay 25. 1927 2 Sheets-Sheet 2 TORNEY Patented Nov. 25, 1930 .UNITED STATES PATENT OFFICE MLANFRED J. JOHNSON, OF BRIDGEPORT, CONNECTICUT, ASSIGNOR TO DICTAPHONE CORPORATION, OF BRIDGEPORT, CONNECTICUT, A CORPORATION OF NEW YORK DEVICE FOR ELECTRICALL Y-RECORDING TELEPHONIC SOUNDS AND CONVERSATIONS AND SYSTEM THEREFOR Application filed May 25,

other telephone lines, or the apparatus usually contained therein, without tapping the line or making electrical connections to a line or its apparatus. This is a particularly advantageous feature, because commercial telephone companies strictly prohibit the making of any electrical connection to their lines ortheir service apparatuson the ground that such electrical connections might detrimentally affect the service or the electrical apparatus of the telephone companies.

This is accomplished, according to the present invention, by inductively picking-up telephonic signals from a telephone line or service apparatus connected in the telephone line such as a telephone-receiver, preferably an auxiliary receiver supplied by the telephone company. Preferably, the pick-up device forms part of a transformer and carries a secondary adapted to be connected to amplifying and/or recording apparatus provided by this invention, while the primary is constituted by the telephone line or service apparatus contained therein. The core of the transformer may be constituted partly by the service equipment and partly by the pick-up device, or it may be supplied entirely by the pick-up device, according to what portion of the commercial telephone system the pick-up device is to be used in connection with.

Likewise, the methods and means of the present invention are advantageous when employed in connection with private telephone lines, for there is a decided advantage in not having to make electrical connections to the service equipment.

Another feature of this invention is the provision of a transforming, rectifying, and amplifying unit by means of which standard, commercial or house current may be used to supply current to the recording device, thus making it unnecessary to use batteries.

And a further feature is the provision of 1927. Serial No. 194,059.

a telephonic signal recording system in which an electric motor operated phonographic replifier interposed between the pick-up device and the electrically operated recorder; 31 rectifier and transformer being shown for heating the filament'of the thermionic amplifierand supplying the plate voltage therefor; and

said transformer being connected to the power lines of standard voltage which is connected to the electric motor for driving the phonographic recorder.

Fig. 2 is a perspective view showing a service telephone instrument and an auxiliary re ceiver, such as is supplied by telephone companies, in inductive relation to a receiver-like pick-up device provided by the present invention, the latter being shown connected to a container for the amplifying device.

Fig. 3 is a sectional view of the form of pick-up device shown in Fig. 2, the receiverlike pick-up device of the present invention being held in inductive relation to the auxiliary receiver by means 'of a suitable clamp.

Fig. 4 is a View similar to Fig. 2, but showing a modified form of pick-up device, the latter comprising a secondary winding and a core adapted to enclose in its magnetic circuit one of the wires of a telephone line, so that the said wire acts as the primary of the transformer.

Fig. 5 is a sectional view of the pick-up device shown in Fig. 4, and shows one form or arrangement of the core which enable. one

wire of the telephone line to be placed in its magnetic circuit.

Fig. 6 is a wiring diagram showing how the system of the present invention may be used in an electric light circuit.

In the art of electric recording of telephonic sounds and signals, many proposals have been made involving the making of electrical connections to the service telephone line or to apparatus contained in the line, but these have not been practicable because of the refusal of telephone companies to permit such connections to be made to their leased equipment. Other proposals have been made using acoustic couplings between the service equipment and electric recording device, but these have involved the use of carbon-grain transmitters which must be handled carefully for they must be made extremely sensitive to be able to pick-up weak telephonic signals.

The present invention overcomes the obj ections of the telephone companies and obviates the disadvantages of the systems using carbon-grain transmitters by inductively picking-up telephonic signals from either the telephone line or from apparatus contained in the line. This method may be carried out by various forms of devices and arrangements,

two of which are shown in the accompanying drawin gs.

One of these arrangements, shown in Figs. 1, 2 and 3, comprises a receiver-like structure which is held in inductive relation to an auxiliary receiver forming part of the telephone equipment. This embodiment of the invention, like those proposals involving the use of a carbon-grain transmitter, requires that a telephone receiver be provided or that it operates in conjunction with a telephone receiver such as is provided by the telephone company. It does not, however, have the disadvantage of the carbon-grain transmitter, namely that of careful handling and being made extremely sensitive, because the electrical undulations or variations are more easily picked-up and these are not transformed into sound vibrations as in the case with the carhon-grain transmitters. Moreover, it is more accurate than a carbon-grain transmit- .er acoustically coupled to a receiver, for in the latter distortion due to the use of two diaphragms and the intervening air-column is unavoidably obtained.

Another arrangement for carrying out the method of the present invention, namely that of picking-up the telephonic signals inductively from the telephone line or apparatus contained therein, is shown in Figs. 4 and 5. In this arrangement, the telephonic signals are picked-up inductively from one of the wires of the telephone line, and hence this arrangement has the advantage that it may be used anywhere that a telephone line is found and does not require any extra equip- 1 ment to be supplied by the telephone company. It comprises atransformer-like structure having a core and a secondary winding wound on the core. The core is arranged to embrace within its magnetic circuit one of the wires of a telephone line, which wire constitutes the primary of a transformer, the secondary being connected to amplifying and/or recordinnapparatus.

The term pic lc-up device is herein used, for the want of a better term, to include any device adapted to receive telephonic signals and transmit them to an amplifying and/or recording device.

The system schematically shown in Fig. 1 comprises a service telephone set A; a pick-up device B; a thermionic amplifier C connected to the pick-up device; a rectifier D; a filter E a multi-tap transformer F; a phonographic recording device having an electrically operated record H, a record mandrel I and a driving motor J; and a source of current supply K.

The telephone set A shown in Figs. 1 and 2, being supplied by the telephone company, comprises as usual a transmitter 10 and a receiver 11 mounted on a base 12 having the telephone wires 13 passing into the instrument at the base. The telephone receiver 11 is provided with a wire 14 leading to the base, and tapped off the wire 14 within the base is a pair of wires 15 leading to an auxiliary receiver 16 supplied by the telephone company usually for those hard of hearing or in cases where there exists considerable extraneous noise. This auxiliary receiver 16 usually comprises a casing 17 in which is mounted a magnet structure 18 having coils 19 on the poles 20 thereof. These coils are connected in series to the wires 15. Usually, the poles 20 are in close proximity to an iron diaphragm which is retained on the casing by a screw-cap and which is vibrated by the magnetic attraction of the poles 20 when voice currents pass through the windings 19.

According to the present invention, however, the cap and diaphragm (not shown) are removed and a receiver-like pick-up device B is brought into inductive relation with the receiver 16. This pick-up device B comprises a casing 21 supporting a magnet structure 22 on the poles 23 on which there is provided a pair of coils 24 connected in series to wires 25 leading to the amplifying and/or recording apparatus. The poles 23 on the pick-up device B are brought into inductive relation with the poles 19 on the auxiliary receiver 16 by placing one against the other so that the poles on both devices touch each other and form a complete magnetic circuit in which condition they are held, according to the present invention, by any suitable means such as for instance a U-clamp 26 having a wingscrew 27 for drawing the auxiliary receiver 16 and pick-up device B together and holding them so in desired relationship.

It will thus be seen that the auxiliary receiver 16. and pick-up device B when placed together as shown constitute a transformer, the primary winding of which is formed by the coils 19 on the auxiliary receiver 16, and the secondary of which is formed by the coils 24 carried by the pick-up device B, the core or magnetic circuit being formed conjointly by the magnet structure 18 and poles 20 of the auxiliary receiver 16 and the magnet structure 22 and poles 23 of the pick-up device B. Hence, when the undulatin gvoice currents corresponding to sound pass through the coils 19,

there is induced in the coils 24 of the pick-up device B corresponding voice currents which are conducted to the amplifying and/or recordin apparatus by means of the wires 25 extendlng from the pick-up device B; Clearly, by placing the pick-up device B in inductive relation to the auxiliary receiver 16, no electrical or direct current carrying connections are made to the telephone equipment, and since the connection is entirely inductive there is no possibility of current flowing through the amplifying and/or. recording apparatus being fed back to the telephone set or its line.

In the form of pick-up device B shown in Figs. 4 and 5, the device comprises a transformer-like structure having a core 28 and a secondary winding 29, the wires 25 from which are led to the amplifying device C. The core 28 comprises a complete magnetic. circuit being in the form of a hollow square as seen in Fig. 5, and is made of two parts one part 28 carrying the secondary 29 and the other part 28 being removably mounted on the part 28 so that one of the telephone wires I 30 may be placed within the magnetic circuit of the parts 28 and 28 when said parts are separated. After the wire 30 is placed within the magnetic circuit of the core 28, the part 28 is returned to the position shown in Fig. 5, in which the magnetic circuit is completed,

- and is held in this position by a pair of clamps 31 pivoted at 32 on the part 28 and provided with thumb-screws 33 by means of which the, clamps are locked in position to hold the part 28 in intimate contact with the part 28*. Thus, a complete transformer is provided, the primary of which is constitutedby a single turn of the wire 30 (although more than one turn may be used if desired) the core 28and the secondary 29.

With this pick-up device B shown in Figs. 4 and 5, it is possible to pick-up telephonic signals anywhere along telephone lines bymerely placing one of the wires Withinthe magnetic circuit of the core 28. Hence, no auxiliary receiver, such as thereceiver 16 shown in Figs. 1 to 3, need be provided, nor is it necessary to cut or scrape telephone wires 30 in order to pick-up the signals. Voice currents passing through the telephone wires 30 induce corresponding voice currents in the secondary 29, and these are passed along by the wires 25 to the amplifying device C. To apply the pick-up device B to the telephone line 30, it is merely necessary to untwist the wires slightly so that the part 28 of the core 28 may be inserted between them. If it is desired to obtain a still stronger signal, the wire may be untwisted a little more and several turn of the untwisted wire wrapped around the part 28 before it is as.- sembled with the part 28*.

This form of the invention is particularly advantageous and useful in recording telephone conversations whereit is desired that the persons holding the conversation be unaware of the fact that the conversation is being recorded. Thus, the device may be used in connection with the detection of crime or for espionage purposes by the duly constituted authorities.

Accordin ,to the present invention, the currents in need in the ick-up device B or B areconducted bya wire 35 to the grid 36 of a thermionic amplifier C, the other wire 37 from the pick-up device B being connected to a negative bias controlling resistance '38 and a wire 39 to the middle leg 40 of a potentiometer 41 connected across the leads 42 and 43 adapted to feed heating current to the filament 44 of the thermionic amplifier C. Voice currents impressed upon the grid 36, when the filament 44 is heated, influence voice currents flow in the plate circuit from the plate 45 to wire 46 leading to the electric recorder H, and-from the electric recorder the plate current, as usual, so that amplified r H through wire 47 to the high voltage contact 81 (marked B+) of the filter E and rectifier D, then from the low voltage or negative contact 83 (marked B of the filter E and rectifier D back to the Wire 39 and then through potentiometer 41 interposed between the leads 42 and 43 of the heating filament 44 of the thermionic amplifier C.

Voice currents, controlled by the thermionic amplifier C and. conducted to the electric recorder H by wires 46 and 47, pass throu h a coil 49 in the core of which is plac an armature 50 mounted for vibratory movements on a bridge 51 secured to pole-pieces 52 and 53 in magnetic engagement with a permanent magnet 54, so that the voice currents, b energizing the armature 50, cause it to vi rate in the air-gaps 55 between it"and the pole-pieces 52 and 53 of the permanent ma et 54. These vibrations are transmitted by a rod 56 to a stylus arm 57 carrying a stylus 58 adapted to engage a record 59 supported by amandrel 60. The vibrations of the armature50 are thus recorded on the wax-like record 59 as it is driven by the motor J through a pulley 61 on the motor, a belt 62 and a pulley 63 on the mandrel 60. i

In order that a single source of current,

such as is diagrammatically illustrated at K, may be made to supply both the motor J and the thermionic amplifier C, both filament heating current and plate current of the latter, the present invention provides a rectifier D and filter E for the plate current and a transformer to supply heating current to both the thermionic amplifier and the rectifier which is preferably thermionic in its action.

As shown in the accompanying drawings, the transformer F has a pair of primary windings 64 and 65. The winding 64 has a secondary 66 connected to the leads 42 and 43 for the filament 44 of the thermionic amplifier C. The secondary 66 is so proportioned with respect of the primary 64 that the proper voltage is obtained across the leads 42 and 43. Thus, the filament 44 is heated by transformed alternating current. The primary 65 of the transformer F has a secondary 67 connected to leads 68 and 69 connected to the filament 70 of the rectifier tube D and is so proportioned that the proper potential is obtained across the leads 68 and 69 for heating the filament 70. In addition to the secondary 67 and cooperating therewith is a secondary 71 having at one side a lead 72 and at the other side a lead 73 tapped off the secondary 67, and thus is in communication with the filament leads 68 and 69 of the filament 70 of the rectifier tube D. The output of the transformer F through the secondary 71 and part of the secondary 69 is rectified by the tube D, the rectified current flowing through the lead 74, filter E, current regulator 48 and 38 to the wire 72 leading to the plate 75 and grid 76 which, in this case, are connected together by wire 77 through the space in the tube D to the filament 70 and from the filament back through the secondary 67 to the wire 73 of the secondary 71.

In the circuit of this rectified current there is interposed a filter E comprising a chokecoil 78 interposed in the wire 72 and parallel condensers 79 and 80 connected across the terminals of the choke-coil and the wire 74 which leads to the plate and grid of the rectifier D.

The potential difference between the contact 81, connected to the wire 72 and marked 15+ and the contact 83 interposed between the voltage regulating resistances 38 and 48, is sufficient to supply plate current of the proper voltage to the plate 45 and filament 44 of the thermionic amplifier C. Likewise. the potential drop between the contact 83 and the contact 82 is sufiicient to make the return circuit for the grid 36 more negative than the filament 44.

Power lines 84 and 85 from the source of current K are connected to both the motor J and the transformer F by means of a single switch 86 interposed between the line 85 and a feed Wire 87 leading to the terminal 88 of the transformer F, a branch 89 going to the terminal 90 of the motor. The power line 84 is connected to the terminal 91 of the transformer F and by a variable contact 92 to a rheostat 93 connected by a wire 94 to the terminal 95 of the electrical motor J which drives the mandrel I for the electric recorder.

Thus, it will be seen that the present invention provides a single source of current from which all the apparatus for electrically amplifying and recording telephonic signals is supplied, and that a single circuit breaker or switch 86 renders the entire device operative or inoperative at will. Clearly, the switch 86 may very conveniently be placed at a point remote from the apparatus, since only two wires need run to the switch, so that signals may be picked-up, amplified and recorded by the apparatus located in one room while the controlling switch 86 is located in another room or it may operate in conjunction with the use of other apparatus. For instance, as shown diagrammatically in Fig. 6, the switch 86 may be used to control a light 96 whenthe wires 84 and 87 may be connected to the light circuit, so that, should the telephone be used at night after office hours, the conversation could be recorded without the person using the telephone being at all aware of the fact. Or, the wires 84 and 87 might be connected across the electric light in a telephone booth having a switch which causes the light to operate when the door is closed, and thus also record conversation over the telephone by unauthorized persons in unauthorized places.

It should be noted that a gas-filled, two electrode tube maybe used, if desired, as the rectifier tube D. However, it is preferable to use the three element thermionic device shown in the drawing, because in such case amplifier tube C and the rectifier tube D may be identical, hence avoiding the danger of an unskilled person getting the tubes mixed up and putting a wrong tube in the wrong place.

Variations and modifications may be made within the scope of this invention, and portions of the improvcmt nts may be used without others.

Having now described the invention, what is claimed as new and for which it is desired to obtain Letters-Patent, is

1 The step in the method of recording telephone signals which consists in mechanically attaching a core and winding in magnetic and inductive relation to the core and winding of a service receiver of a service telephone system to provide a transformer for picking up sound produced currents.

In a device for recording telephonic signals transmitted over a service telephone system having a coil forming part of its receiving apparatus, the combination of an electrically operated phonographic recording means; and signal pick-up means for tion 0 controlling said recording means, said pickup means comprising means inductively asso'ciated with the said coil of said receiving apparatus. a

3. In a device for recording telephonic signals transmitted over a service telephone system having a magnet forming part of its receiving apparatus, the combination of an electrically operated phonographic recording means; and signal pick-up means for controlling said recording means, said pickup means comprising means electroma etically associated with the said magnet 0 said receiving apparatus.

4. In a device for recording telephonic signals transmitted over a service telephone system having a service receiver forming an inte al part of the system, the combinaan electrically operated phonographic recording means; pick-up means comprising a receiver-like structure having a core and winding placed in electromagnetic relation to said service receiver, and constituting with said service receiver an inductive coupling transformer, the primary of which is formed by the winding of the service receiver, the core of which is formed by thecore of the service receiver and the core of the receiver-like structure, and the secondary of which is formed by the winding on the receiver-like structure; and means for controlling said phonographic recorder by voice-currents induced in the winding of the receiverlike structure by the service telephone voicecurrents flowing through the service receiver.

5. Ina device for recording telephonic signals transmitted over a service telephone system having a service receiver comprising a magnetic core and winding forming an integral part of the system, the combination of electrically operated phonographic recording means, pick-up means com rising a magnetic core avin a winding-t ereon adapted when said core is brought mto proximit with the core of said service receiver to ave voice-currents corresponding to voice-currents existing in said receiver induced in said winding, and means for controlling said recording means by the voicecurrents induced inthe said windin 6. In a device for recordin tefiephonic signals transmitted over a servlce telephone system having a service receiver comprising a ma netic core and winding forming an into a part of the system, the combination 0 an electrically operated phonographic.

means, pick-up means comprising a magnetic core havin a winding thereon and adapted when sai core is brought into proximity to said service receiver to have voiceing, a thermionic device controlled by the voice-currents induced in the said winding,

and means connectin the thermionic device with said phonograp ic recorder. I

7. In a device for recordin telephonic signals transmitted over a service telephone system having a service receiver comprising a magnetic core and winding forming an integral part of the system; a receiver-like structure having a magnetic core and winding juxtaposed with and inductively coupled to the said service receiver; and means for holding said service receiver and receiverlike structure in juxtaposed position.

Si ed at Bridgeport, in the county of Fair eld and State of Connecticut, th1s 24 day of May, 1927.

I MANFRED J. JOHNSON. 

